Woo Hyoun Sik, Kim Kil Joong, Kim Tae Jung, Hahn Seokyung, Kim Bohyoung, Kim Young Hoon, Lee Kyoung Ho
Department of Radiology, Seoul National University Bundang Hospital, 300 Gumi-dong, Bundang-gu, Seongnam-si, Gyeonggi-do, Seoul 463-707, Korea.
AJR Am J Roentgenol. 2007 Sep;189(3):535-41. doi: 10.2214/AJR.07.2304.
The purpose of our study was to compare the tolerance of Joint Photographic Experts Group (JPEG) 2000 compression between thin- and thick-section abdominal CT images.
One hundred 0.67-mm-thick and corresponding 5-mm-thick images were compressed to four different levels: reversible and irreversible 6:1, 10:1, and 15:1. Five radiologists determined if the compressed images were distinguishable from the originals. The percentage of distinguishable pairs and peak signal-to-noise ratio (PSNR) were compared between the thin and thick sections. The visually lossless threshold was estimated by comparing the percentages of the distinguishable pairs between each irreversible compression and the reversible compression. Paired Student's t tests and exact tests for paired proportions were used.
Thin sections had smaller PSNRs at each compression level (p < 0.001). According to the pooled responses, the percentages of distinguishable pairs for the thin and thick sections, respectively, were 0% (0/100) and 0% at reversible compression, 27% and 0% at 6:1 (p < 0.001), 100% and 80% at 10:1 (p < 0.001), and 100% and 100% at 15:1. Artifacts increased significantly (p < 0.001) at 6:1 or more for the thin sections and at 10:1 and 15:1 for the thick sections, indicating that the visually lossless thresholds were below 6:1 and between 6:1 and 10:1, respectively.
Thin-section abdominal CT images are less tolerant of compression, and a lower compression level should be used for the visually lossless threshold.
我们研究的目的是比较腹部薄层和厚层CT图像对JPEG 2000压缩的耐受性。
将100幅0.67毫米厚及相应的5毫米厚的图像压缩至四个不同级别：可逆和不可逆的6:1、10:1和15:1。五名放射科医生判断压缩后的图像是否可与原始图像区分。比较薄层和厚层图像中可区分图像对的百分比及峰值信噪比（PSNR）。通过比较每种不可逆压缩与可逆压缩之间可区分图像对的百分比来估计视觉无损阈值。采用配对t检验和配对比例的精确检验。
在每个压缩级别，薄层图像的PSNR较小（p<0.001）。根据汇总的结果，可逆压缩时，薄层和厚层图像中可区分图像对的百分比分别为0%（0/100）和0%；6:1压缩时分别为27%和0%（p<0.001）；10:1压缩时分别为100%和80%（p<0.001）；15:1压缩时分别为100%和100%。对于薄层图像，在6:1及以上压缩时伪影显著增加（p<0.001），对于厚层图像，在10:1和15:1压缩时伪影显著增加，这表明视觉无损阈值分别低于6:1和介于6:1与10:1之间。
腹部薄层CT图像对压缩的耐受性较差，对于视觉无损阈值应采用较低的压缩级别。
